FTDI, in generic electronics use, refers to an interface. (In fact, that's what the I at the end of FTDI stands for.) So an "FTDI chip" is different from an "FTDI(tm) Chip." Electronic interfaces are not patentable or copyrightable, AFAIK. The 'fake' FTDI chips don't necessarily represent themselves as FTDI(tm) Chips, and certainly don't use the same designs -- it's just that they take the same inputs and put out the same outputs. Misrepresenting your PID to a driver is not the same as counterfeiting -- it's breaking a USB(tm) rule, but if you're not a party to those rules, there's no legal onus to not do so. It's basically the same thing as an x86 compatable PC chip -- it may be made by AMD, but it'll accept the same inputs and spit out the same outputs from those inputs as an Intel chip, even though the internal architecture may be significantly different.